When broadcasting radio, the LF signal (Low Frequency = speech, music) must be turned into something that can be transmitted across a big distancd.
To do this, radio emitters use a carrier wave to transport the audio signal. This wave is a high frequency signal which is fixed for each broadcasting site. In our case, we receive Option Musique on 765 kHz.
So, the sender applies the audio signal on the carrier wave, which is called amplitude modulation (AM).
The receiver has to oscillate on the same frequency as the transmitter it wants to receive. This oscillation is created by the variable condensator and the inductivity, which then receive the modulated signal.
The diode then will dispose of half of the wave, which is called the demodulation.
This demodulated signal can then be heard with a speaker of high impedancy, about 1 kOhm.
Would the signal not be demodulated it could not be heard because the two halfs of the wave would compensate each other.
